Electronic Slope Detector

This invention relates to a device for determining the orientation of a surface relative to the horizontal.

Many applications require determining the orientation of a surface or plane. The well known manual gravity bubble level is one device to accomplish this task.

One specific application where the orientation of a surface is critical is automatic drilling and riveting of panels on an aircraft. Ideally, the rivet hole should be drilled normal to the surface being riveted for greatest effectiveness. However, the surface is often continuously curved in multiple directions, particularly when forming part of the wing structure.

The compound curvature of the skin structure makes it difficult to use a traditional manual level. Further, the market place demands significant automation in the process to reduce cost. Therefore, a need exists for a device to more effectively and efficiently determine the level of a surface to be riveted.

In accordance with one aspect of the present invention, a device is provided for determining the three dimensional orientation of a surface external to the device with regard to a reference plane. The device includes a body and at least three sensors mounted to the body at locations thereon which are spaced apart from each other so that the locations of the sensors define the reference plane. Each of the sensors provide an electrical signal which represents the distance from the respective sensor to the surface external to the device. An electrical processing circuit receives each of the electrical signals from the sensors and provides an indication of the orientation of the surface with respect to the reference plane.

In accordance with another aspect of the present invention, the sensors provide an electrical signal which represents the distance from the respective sensor to the surface along a line which is perpendicular to the reference plane. The sensors can provide an electrical signal representing the distance from the respective sensor to the surface without the respective sensor touching the surface.

In accordance with another aspect of the present invention, each sensor can include a sensor body, a probe element and structure for biasing the position of the probe element with respect to the sensor body along a line having a predetermined orientation to the reference plane. The structure can provide an electrical signal representing the position of the probe element with respect to the sensor body.

In accordance with another aspect of the present invention, the sensors can be ultrasonic, laser, low voltage differential transformers (LVDT) or potentiometer devices.

For a more complete understanding of the present invention, and for further advantages thereof, reference is now made to the following Detailed Description taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a side view of a surface and a portion of a sensor device forming a first embodiment of the present invention to detect the orientation of the surface;

FIG. 2 is a top view of the surface showing the position of the three sensors;

FIG. 3 is a block diagram of the function of the sensor device;

FIGS. 4A and 4B are a detailed schematic of the operation of the sensor device; and

FIGS. 5A and 5B are a flow chart of the computer program used to process the sensor position data and calculate the angular orientation for display.

FIG. 6A and FIG. 6B are illustrative views of the body showing the sensors thereon.

With reference now to the accompanying drawings wherein like reference numerals designate similar parts throughout the several views, an automated electronic bubble level 10 forming a first embodiment is illustrated. The electronic bubble level 10 is used to determine the angular orientation of a part surface 12 relative to gravity and to display that relation on an output display 14.

The electronic bubble level 10 includes a body 16 having three sensors, a right rear sensor 18, a right front sensor 20 and a left sensor 22. The sensors are used to determine the orientation of three spaced points on the parts surface as seen in FIG. 2 and uses those three points 28, 30 and 32 to define a reference plane 24 which will be at an angle corresponding to the surface at the point 26 to be riveted or drilled. Body 16 can be a drill which has a drill bit extending therefrom to drill along an axis perpendicular to the reference plane.

FIGS. 6A and 6B illustrate the bubble level 10 mounting the sensors 18, 20 and 22 thereon. FIG. 6B illustrates the mounting of a drill bit 33 on the mobile level 10 to perform a drilling operation.

With reference to FIGS. 1 and 2, the right rear sensor 18 can be seen to determine the position of point 28, the right front sensor 20 is used to determine the position of point 30 and the left sensor 22 is used to determine the position of point 32 on the part surface 12.

With reference to FIG. 3, the output of the sensors 18, 20 and 22 is provided to a microcontroller 34 which electronically defines the reference plane and transmits that information through a display driver 36 for display on an LED dot matrix chip 38.

The sensors 18, 20 and 22 can be of many different constructions. For example, the sensors can be ultrasonic, laser, low voltage differential transformer (LVDT) or potentiometer devices. Thus, the sensors do not even need to be in contact with the part surface 12 when using devices such as ultrasonic or laser sensors.

With reference now to FIGS. 4A and 4B, the details of one device constructed in accordance with the teachings of the present invention will be described. FIGS. 4A and 4B illustrate a schematic of the device. A power supply, not shown, provides a +5 volt line 40 and a ground line 42. Each of the sensors 18, 20 and 22 is a 5 kilo ohm potentiometer with a wiper arm 44 which is positioned as a function of the location of the point, 28, 30, and 32, respectively. The line from the wiper arm of the right rear sensor 18 is line 46. The line from the wiper arm of the right front sensor 20 is sensor line 48. The line from the wiper arm 44 of the left sensor 22 is sensor line 50. These lines, and the power supply lines, are connected through a connector 52 to the input of microcontroller 34. The microcontroller is a New Micros, Inc. No. NMIS-0021. The microcontroller has been programmed with a program known as Bublevel .S19 which takes the input data of sensor positions from sensors 18, 20 and 22 and calculates the position of a plane containing all three points sensed by sensors 18, 20 and 22. FIGS. 5A and 5B are a flow chart of the control functions of the microcontroller. While a specific microcontroller is mentioned above, it will be understood that any suitable controller can be utilized. The controller begins with a start step 150 which leads into an initialization routine 152. Step 154 then reads sensors 18, 20 and 22 and calculates errors. Step 156 then asks the question if the sensors are to be calibrated. If so, step 158 is taken to calibrate the sensors and the program is returned to step 154. If not, step 160 then asks if the sensitivity is to be fine. If yes, step 162 is the set up for fine sensitivity. If not, step 164 is the set up for coarse sensitivity. After sensitivity determination, step 166 is the calculation of the angular errors. Step 168 decodes the X axis part angle and step 170 decodes the Y axis part angle. With reference to FIG. 5B, step 172 downloads the X and Y angle data to the display. Step 174 represents the return to the initial start of the program for scanning sensors. A print out of a program for use on the microcontroller noted above is set out on the pages hereof immediately prior to the claims. The +5 volt line 40 is connected to the +5 volt terminal and the VRH terminal on the controller 54. The ground is connected to the ground terminal and VRL terminal on the controller 54. The sensor lines each pass through a resistor, having resistance of 5 kilo ohms, to ports PE0, PE1 and PE2 in the controller 34.

The +5 volt line is also connected to a calibration circuit 56 and a sensitivity fine/coarse circuit 58. In the sensitivity circuit 58, the coarse selection determines slope at increments of .+-.2, 4, 6 and 8 degrees in both the left/right direction and the forward/reverse direction. The fine sensitivity selection measures .+-.1, 2, 4 and 6 degrees in both the left/right direction and the forward/reverse direction.

The controller 34 will analyze the input from the sensors and will create a reference plane on which the three points 28, 30 and 32 lie. Since the three points are spaced apart, only one unique plane will contain all three points. The controller 34 will then determine the slope of this reference plane, which will correspond to the slope of the part surface at the point 26 being measured. The calculated slope is then displayed on the bubble level display chip 38.

To accomplish the display, the controller 34 outputs a +5 volt line 60, a ground line 62, lines 64, 66 and 68 and display lines 70-84. The lines are connected to a pair of octal transparent free state latches 86 and 88, each latch being a 74HC373 integrated circuit. Each line is connected to ground through a resistor 90 having a value of 10 kilo ohms for the purpose of pull down resistance. Inputs to 74HC373 devices will float without these resistors.

Output from the latches 86 and 88 are provided to the 5.times.7 dot matrix display chip 38. The chip is a Model HDSP-4501 manufactured by Hewlett-Packard. The lines from latch 86 each pass through a resistor 92 having a value of 470 ohms to the row input of display chip 38. The purpose of this resistor is current regulation which controls LED intensity. The output from latch 88 goes to the column input of chip 38. The dot matrix chip display 38 defines a 5.times.7 matrix of LEDs. This display will give a visual display of the slope of the surface being measured.

As can be seen, the device of the present invention will define a reference plane electronically and display the slope of that reference plane to the user. This slope corresponds to the slope of the surface of the point 26. Therefore, if a hole is to be drilled at point 26, the drill bit can be positioned precisely normal the surface to be drilled, preventing the drill bit from being deflected or skipping off of the point and insuring an effective hole is drilled through the material for subsequently receiving a rivet.

Although one embodiment of the invention has been illustrated in the accompanying drawings and described in the foregoing Detailed Description, it will be understood that the invention is not limited to the embodiment disclosed, but is capable of numerous rearrangements, modifications and substitutions of parts and elements without departing from the spirit and scope of the invention.